The present invention relates to a process for producing a fibrous, modified polytetrafluoroethylene. More particularly, it relates to a process for producing a fibrous, modified polytetrafluoroethylene having a homopolymer of tetrafluoroethylene as a core and a copolymer having functional groups as a sheath layer the particles are prepared by homopolymerizing tetrafluoroethylene in the first step and then, copolymerizing tetrafluoroethylene and a fluorinated modifier having a specific functional group in the later step, preferably using emulsion polymerization. The polymerization step is taken past the Kraft point to assure that the particles are coagulated and coalesced to form a highly porous, fibrous, stratified fluoropolymer with a plurality of interconnected, three-dimensional fibrous-like projections.
In general, processes are known for using emulsion polymerization to form stratified polymeric particles. For example U.S. Pat. No. 4,326,046 teaches such a method. However, the particles produced according to the method of the '046 patent are inferior in their acid catalyst properties of the materials produced according to the present invention.